Exponential dependence of interlayer exchange coupling in Fe/MgO(001) superlattices on temperature

The interlayer exchange coupling in Fe/MgO(001) superlattices is found to increase exponentially with decreasing temperature. Around 150 K, the field-induced response changes from discrete switching—governed by field-driven domain propagation—to a collective rotation of the magnetic layers. This transition is accompanied by a change in the magnetic ground state from <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msup> <a:mn>180</a:mn> <a:mo>∘</a:mo> </a:msup> </a:math> (antiferromagnetic) to <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msup> <b:mn>90</b:mn> <b:mo>∘</b:mo> </b:msup> </b:math> alignment between adjacent Fe layers. These effects are argued to arise from quantum-well states, defined by the total thickness of the samples.